This invention relates to flowable nanoparticles which can be used for printing images.
Ink jet printheads are used to selectively eject ink droplets onto a receiver to form an image. Within the printhead, the ink may be contained in a plurality of channel members and energy pulses (either piezo or heat) are used to actuate the printhead channel members or the ink orifices causing the droplets, which form the reservoirs, of ink to be ejected on demand or continuously, through an orifice plate which is placed over the channel members.
In one representative configuration, a piezoelectric ink jet printing system includes a body of piezoelectric material defining an array of parallel open topped channel members separated by walls. In the typical case of such an array, the channel members are micro-sized and are arranged such that the spacing between the adjacent channel members is relatively small. The channel walls have metal electrodes on opposite sides thereof to form shear mode actuators for causing droplets to expel from the channel members. An orifice defining structure includes at least one orifice plate defining the orifice through which the ink droplets are ejected, and is bonded to the open end of the channel members. In operation of piezoelectric printheads, ink is directed to and resides in the channel members until selectively ejected therefrom. To eject an ink droplet through one of the selected orifices, the electrodes on the two side wall portions of the channel in operative relationship with the selected orifice are electrically energized causing the side walls of the channel to deflect into the channel and return to their normal undeflected positions when the applied voltage is withdrawn. The driven inward deflection of the opposite channel wall portions reduces the effective volume of the channel thereby increasing the pressure of the ink confined within the channel to force few ink droplets, 1 to 100 pico-liters in volume, outwardly through the orifie. Piezoelectric ink jet printheads are described in detail in U.S. Pat. Nos. 5,598,196; 5,311,218; 5,365,645, 5,688,391, 5,600,357, and 5,248,998. Alternative ink jet print head configuration utilizes thermal energy to eject ink droplets from the orifices onto the receiver. Thermally activated ink jet print heads are described in details in U.S. Pat. Nos. 4,849,774; 4,500,895; and 4,794,409. This process of forming channel members, particularly in piezoelectric materials, is not only time consuming and expensive, but also is amenable to many defects generated during cutting the channel members or forming the channel members thereby reducing the throughput and increasing the unit manufacturing cost. Furthermore, mechanical damages caused during sawing or laser cutting also are detrimental to the piezoelectric characteristics of the material.
Another significant problem encountered in ink jet printing is the drying of the ink either inside the channels or at the orifice plates or at the orifices. To overcome this problem the ink formulators routinely compromise in ink formulations and the system designers incorporate wiper blades at the orifices or depend on ultrasonic devices to clean and remove the dried ink. Again, this introduces additional complicated system architecture and consequently increases the unit manufacturing cost.
Inks provide their own set of problems in ink jet printing, they are at all times flowable, thus subject to leakage, and may have storage problems, including limited shelf life. They also have a problem of drying and difficulty maintaining uniform viscosity since they can be temperature sensitive. Inks have been formed which have numerous ingredients such as dyes, pigments and colorants and nanoparticles (see U.S. Pat. No. 5,679,138). But, in all cases, the ink remains flowable in all states and subject to problems.
It is an object of the present invention to provide an improved material which is not a flowable ink that can be used for forming images.
This object is achieved by using an image producing material which when deposited on a receiver produces an image comprised of nanoparticles selected to have an average diameter of less than 500 nm and arranged so as to be effective in two states, in a first state it aggregates and will not flow through an ink jet printer nozzle and in a second state when subject to a force is flowable so as to be deposited on the receiver, such nanoparticles being bound to each other by Van der Waals forces in the first state and after deposition on the receiver.
It has been discovered that nanopaiticles which are effective in two states can be used to form images on receivers. Nanoparticlcs having an average diameter of less than 500 nm aggregate because of Van der Waals forces and are not flowable past an orifice in a first state but are flowable in a second state when a force as been applied to overcome the Van der Waals forces. A feature of the invention is that a stream of gaseous material, such as air, can be directed so as to cause the flow of Such nanoparticles towards the receiver.
The nanoparticle imaging materials used with this system have no vapor pressure and hence will not dry out and clog, eliminating the need for such complexity in the print head. The present invention provides a simple solution to ink clogging problems and facilitates the use of smaller orifices. Smaller orifices can provide greater resolution. Additionally, the speed of the ink jet printer system can be increased because there is 110 fluid component to the nanoparticle imaging materials which eliminates the need to wait for solvent drying on the receiver, a major limitation in ink jet printers.